DEVELOPMENT OF THE EMBRYONIC lU'lHMENT — OCTOPUS. 



265 



that the Octopoda must be regarded as derived and the Decapoda as 

 primitive forms. The conjecture as to the nature of these promin 

 ences is further rendered probable by the fact that tins occur in some 

 adult Octopoda (Octopus menitoanaceux, Pinnoctopus, Girrhoteutliis). 



The oral aperture appeal's in Octopus at a very early stage and 

 SOOl) takes the shape of a semicircular groove bordering a swelling. 

 The appearance of the rudiments that lie on the ventral side closely 

 resembles that described for Loligo and will best he understood h\ 

 a study of Fig. [22 A and B, and by comparing this figure with the 

 illustrations of the Loligo embryo given in Figs. 117 and lis. 



It should be noted that the funnel forms, in the Octopoda, in the 

 same complicated way as in Loligo and the other Decapods. A paired 

 posterior fold appears and, in the course of development, unites with 

 an anterior fold which is also paired to form the funnel and its lateral 

 parts (Figs. 122 and 123, hff, vtf and /•/). 



Fig, 122. — Two embryos of Octopus vulgaris at different ages, seen from tin- posterior 

 side (original). ar, arms : aw, optic swellings ; ds, yolk-sac ; htf, posterior funnel- 

 told ; / , ui]l> : /". mantle ; "'. otocysts ; vtf, anterior funnel-fold. 



In comparing Loligo and Octopus, we are struck by the tact that, in the 

 latter, the separate organs appear very early, hut do not develop further with 

 corresponding rapidity, so that, as contrasted with organs that appear later, 

 their development is retarded. This peculiarity was pointed out by Brooks 

 (No. 7), in comparing the form examined by him (Loligo Pealii) with 

 Grenacher's Cephalopodan embryo. In Octopus, for instance, the rudi- 

 ments of the arms appear early, their number being complete even earlier 

 than the stage depicted in Fig. 122 .!, hut they then develop very slowly. 

 With regard to the order in which the arms appeal 1 . this seemed to us to be 

 the same as in Loligo, i.e. from the rudiment of the funnel towards the 

 mouth. Two pairs of arm- appear :i- slight swellings in front of. the optic 



